This project aims to advance our understanding of the association between provider volume, and the costs and quality of cancer surgery. Previous studies have found that surgeons and hospitals that perform more cancer operations per year have lower operative mortality rates (9-13). This relationship exists for complex operations such as pancreatic resection, and for more commonly performed procedures such as colectomy. We recently published a study that found that relative to low-volume surgeons, treatment by high-volume surgeons was associated with lower per-patient hospital costs for six different cancer resections. However, high hospital volume was associated with lower hospitals costs for only one procedure, colectomy (14). This project seeks to determine the underlying reasons for these findings by answering the following questions: 1) What is the association between provider volume and both physician and hospital costs, separately and combined? 2) What are the factors that are associated with lower costs for high-volume surgeons? 3) What factors determine costs for hospitals? 4) What is the differential between Medicare reimbursement and costs for low and high volume hospitals? Does hospital profit vary by provider volume status? 5) Are the factors associated with lower costs for surgeons/hospitals also correlated with lower mortality rates for patients? The results have important implications for identifying cost-effective approaches to providing cancer surgery. The analyses will shed light on whether referring patients to high-volume providers, lowering DRG reimbursement rates to discourage low-volume providers, or dissemination of best practices irrespective of volume could restrain cost growth and improve patient outcomes. PUBLIC HEALTH RELEVANCE: Gaining insights on why the number of cancer operations that hospitals and surgeons perform is associated with the costs of patient care will enable us to determine whether centralizing complex cancer operations will restrain the rising costs of cancer care. Moreover, we know relatively little about which processes of care or other factors influence patient costs. By identifying some of these factors, we will provide knowledge which can guide efforts to achieve process improvement that will both improve patient care and save costs.